Temperature responsive control



June 2', 1953 c. A. COBB 2,640,313

TEMPERATURE RESPONSIVE CONTROL Filed Sept. 12, 1947 Lvl/Europ:

C?. /FroN A. C055 Patented June 2, 1953 UNITED sifrlrs PATENT OFFICE2,640,313 TEMPERATURE Ims1 oi'\TsIvE CONTROL Clifton A. Cobb, UniversityCity, Mo., assigner Vto Missouri Automatic Control' Corporation, St.Louis, Mo., a corporation ofMissouri Application september 12, 1947;sei-inno. 773,646

(Cl. (iO-) 6 Claims.

This'invention relates to temperature responsive controls andparticularly to those suitable for high temperature use such as in thedetection of flame at a burner. I

It is an objectof the present inventionto provide a novel'and reliabletemperature lresponsive device suitable for flame detection use,employing a yfluid having liquid forin at normaltemperatures, and inwhich the control is actuated by the pressure-volume change ,due to thevaporization of a portionof the iiuid at certain temperatures. A furtherobject is to provide in a device of this character, means ,vhereby thepressure-volume change required to operate the control and therefore thetemperature at which it will operate, may be predetermined and variedWithin a range above the normal atmospheric boiling point of the uuid.

It is a further object to provide a temperature responsive controlhaving a temperature sensitive bulb and a remote expansible chamberconnected thereto by a conduit to form a closed system, which systemcontains a liquid in suiicient quantity so that rthere is an'amount ofliquid forced into the bulb when the expansible chamber'is initscontracted position, and in which the liquid is displaced from thebulb by vaporization of a 'relatively small portion thereof at apredetermined temperature to expand the remote expansible chamber andthereby actuate a control means,

It is a further object to provide a device of this character in whichthe communicating passage between the bulb and the expansible chamber ishighly restricted, and in `which the expansible chamber is expansibiefrom its contracted position sufficiently to receive all of said Aamountof liquid in' the bulb so that the liquid may be completely expelledfrom the bulb when it is sumo'iently heated, whereby the liquid vaporphase occurs in the highly restricted passage, thereby to minimize itssurging eifect' upon the expansible chamber.

It is a further object to provide a device of this character in whichthe liquid filled bulb having a single opening for communication withthe expansible chamber is so constructed and arranged that theopeningiscovered by liquid until all liquid displaced therefrom by the pressureof a vaporiaed portion thereof.

Further objects and advantages will appear upon reference to thefollowing description and accompanying drawing.

in the' drawing,

Fig, 1 diagrammatically .illustrates one form oi the present inventionin use as a safety fuel cutoi-d'evice'sensitive to'v flame at a vpilotburner;

nFig.r2`l`is an enlarged cross-sectional view of the combined.'sv'vitching mechanism and expansible chainb er shovvn Y inFigure 1Fig. 3 vis'anenlarged cross-sectional view of the temperature sensitivebulb shown associated with the pilot burner' in `Fig. 1. l

ln Figure 1a main Iburr'ier isindi'cated in'y part at lll'iand a pilotburneris indicatedat H. Fuel is rsupplied to the mfainan'dpilot burnersthru the conduit I2 andthe branch i3. The fuel supply rvto lboth burnersis controlled by fan electromagneticv valve i4 which when energizedmoves to anopen position tofpermit'rfuel to flow' to the burners andupon deenergiz'ation closes by gravity or by spring to cut off `allrfuel tothe burners. A manual means'for opening valve I4 is provided andis indicatedat'llal 'The fuel supply to the main "burnerfor intermittentvoperation as required'is controlled by al suitable valve l5. The valveIll is energized by a circuitconsisting of the leads' I5 and l1,"v`vhi`ch are connected to a'suitable source ofelectrical energy (notVshown), and the circuit isbontrolled bya switchgenerally indicated atI3. The switch i8 is yactuated by a ternperaturey responsive deviceconstructed in accordance 'with the present invention. The devicecomprises a ybulb l5 `Wh`ich is arranged to be heated by the'pil'otburner flame, anexpansible chambergenerallyiindicated at 20, and aconnecting capillary'tube2 l.- y n The expansible chamber lconsists ofan outer heavy ivalledcuprnember 22 'and an'inner thin Walled fleiiible`'cup member 23. The Side walls ofthe innerand outer cups are joined byconinuo'us Welding as indicated at 2liv to form a high pressure fluidtightfseal. There is an opening 25 in the outer cup which receives oneend of the capillary tube 2 l. The tube is therefore inconiinunicationwith the space'betvveen the bottom Walls of thecupsu Thetube is suitably attached tocurp 22 byfwelding. it its other end thecapillaryt'ube is connected to the temperature sensitivebulb l 9 whichbulb is attached in an upright positiongas indicated, to) the pilotburner by any suitablern'eans, as the clamp 26.

The bulb haga chamber 21 formed in its upper portion and a concentricvlongitudinal bore 28 exteilidingjthruits flower portion which is sizedto receive the capillary' tube in close fit relationship. 'The'capillaryis inserted` to the point of junctionyof the chamber '2] and bore 28 andthe lovver lend of the charnberZlk is tapered so as to avoid anycornersA Which'may entrap liquid. The

3 capillary is attached within the bulb by welding the tube to the wallsof the bore 28 thereby to form a high pressure fluid seal.

The expansible chamber 2D is attached to a plate member 29 by screws 30.Plate 29 has a central bore 3i which receives in sliding t relationshipan actuating pin 32. One end of pin 32 is held against inner cup 23 by aspring 33. The other end of the pin 32 bears against a switch arm 34.The pin is provided with an insulating tip 35 and the switch arm 34 isprovided with a leaf spring 33 to provide for overtravel after thecontacts are closed. The spring 33 may be adjustably tensioned byrotating the threadedly adjustable collar 33a on the pin 32. The switcharm is pivoted at 31 in a casing 39 and carries a movable contact 33adjustably mounted at its free end. A fixed contact 40 is mounted in thewall of the casing 39. Terminal connections 4i and 42 are mounted in thecasing wall for attachment or' leads I6 and I1, and a pig-tailconnection 43 is provided between terminal 42 and the switch arm. Theswitch arm is urged in a clockwise direction by a spring 44 andtherefore the switch is biased in a circuit breaking position. It willbe understood that the leaf spring 3G is much stronger than the spring44.

The expansible chamber is shown, in Figure 2, in its fully expandedposition in which the volume between the walls of the cups issubstantially equal to the volume of the bulb chamber 21. In itscontracted position, to which it is urged by the spring 33, the walls ofthe cups come into contact and the volume is substantially zero. Withthe expansible element in a contracted position the system is exhaustedof air and filled with a high boiling point liquid.

Experiments indicate mercury to be the preferred liquid, because it isstable at high temperatures, it is heavy and gravitates well to theopening in the lower end of the bulb chamber, and because its boilingpoint is high enough so that heavy loading of the spring 33 is notrequired to maintain the operating temperature of the device safelyabove temperatures which may occur ambient to a burner in a furnace.

It will be seen that the bulb 21 is so constructed and positioned that,upon boiling of the liquid, vapors will rise to the upper end, and asvaporizing progresses, the liquid will continue to cover the opening atthe lower end of the chamber until al1 liquid is forced from the bulb.It is imperative that the opening is at the lowest point of the bulbchamber, otherwise liquid will continue to gravitate into the chamberwherein it will be vaporized causing unduly high pressures and erraticoperation. The expanded volume of the expansible chamber being at leastequal to the bulb chamber 21, the chamber may therefore receive all ofthe liquid in the bulb and the liquid-vapor phase or the point at whichthe liquid is boiling will therefore occur in the capillary tube whenthe bulb is suiiiciently heated. The internal diameter of the capillarytube is exceedingly small relative to the diameter of the bulb chamberand therefore the effect of this agitation on the expansible element isreduced to a minimum. It is obviously necessary to arrange the bulb sothat all of chamber 21 is sufliciently heated, at least as far as thejunction with the capillary tube, in order to completely displace liquidfrom the chamber 21 and to insure that the point of boiling occurs inthe capillary tube. In the present use of the device, wherein the bulbis directly impinged by flame, the design 4 of the burner port and thedisposition of the bulb relative thereto should be such that the ameplays on a sufficient portion of the bulb, to insure this, as isindicated in Fig. l.

The strength of spring 33, which urges the pin 3| toward the right andthereby urges the expansible element toward its contracted position,determines the temperature at which the contacts 38 and 40 are closed.As the strength of the spring is increased, the pressure in the sealedsystem is increased and the boiling point of the liquid is therebyraised. By increasing the tension of spring 33 the temperature at whichthe contacts are closed can be raised above any anticipated temperaturelikely to occur ambient to the burner. By constructing the expansibleelement so that it will operatively expand suciently to receive all ofthe mercury in liquid form from the bulb chamber, excessive pressures,which would otherwise occur upon further heating and which would requiremassive structure to Withstand, are avoided.

In operation When in a cold or no-flame position, the positions of theelements of the device will be as follows: the inner and outer walls ofthe expansible element will be contiguous due to the pressure of spring33 and the liquid will fill the bulb and the capillary tube. The switcharm 34 will be rotated clockwise by the spring 44 and the contacts 38and 40 will be open and the energizing circuit for the electromagneticvalve I4 will be open causing all fuel to the burner to be cut oil.

In order to light the pilot burner under these conditions the valve I4is opened manually by the manual means I4a and is held open as the pilotburner is ignited and thereafter until the contacts 38 and 40 are closedto complete an energizing circuit for holding the valve open. As theburner is ignited the temperature of the liquid in bulb 21 will riserapidly until a portion thereof vaporizes. Prior to reaching the boilingpoint, there will of course be a slight expansion of the liquid, butthis increase in volume is negligible in its effect upon movement of theswitch arm because of the proportioning of the instrument. In the caseof mercury for instance, the volume increase from 32 F. to 676 F. (theatmospheric pressure boiling point) is less than 7 per cent, while thevolume increase from liquid to saturated vapor at 850 F'. (which is inthe order of the temperature at which the control would be operated inilame detection use) is approximately 850 times. After the boiling pointis reached expulsion of the liquid from the bulb progresses rapidly withrelatively slight temperature increase and at some point before theliquid is completely expelled from the bulb the switch arm will be movedcounterclockwise suiliciently to close the contacts. Expansion of thechamber beyond this point so as to permit complete expulsion of theliquid from the bulb is provided for by the overtravel spring 36 carriedby the switch arm. The device will thereafter remain at a circuitclosing position as long as the ilame at the burner is maintained.

If for any reason the flame at the pilot burner is extinguished, thetemperature of the bulb drops rapidly to a point below the boiling pointof the mercury at the instant pressure and the liquid is expelled fromthe expansible chamber under the pressure of spring 33, and switch arm34 moves clockwise to break the circuit under the urging of spring 44.It will be seen that during the initial contracting movement of theexpansible element following flame failure the spring 36 will retain thecontacts at a closed position. The provision of the overtravel spring 36and the adjustable mounting of contact 38 permits varying the timerequired to make or break the contacts after ignition or extinguishingof the flame.

The aforegoing description is intended to be illustrative and notlimiting and the exclusive use of all modifications within the scope ofappended claims is contemplated.

I claim:

1. A burnerk safety device adapted to use in high ambient temperaturesfor detecting the presence or absence of flame at a burner: comprisingan expansible chamber, a bulb portion spaced from said expansiblechamber for disposition at the flame, a tube connecting the bulb portionand expansible chamber so as to complete a closed system, the systembeing lled with a high boiling point liquid charge when said expansiblechamber is in a contracted position, said liquid charge having a boilingpoint of at least 600 Fahrenheit, and said expansible chamber beingexpansible from its contracted position to receive the amount of liquidcontained in the bulb portion of the system when the bulb portion isheated suiciently by flame to complete the expulsion of all liquidtherefrom, whereby a large rapid expansion or contraction of theexpansion chamber occurs as the bulb temperature rises slightly above orfalls slightly below the boiling point of the fiuid therein, controlmeans having first and second operating positions, and being connectedto said expansion chamber to be moved by expansion and contractionthereof, the said positions being separated sufficiently to require thelarge volumetric change caused by a change of state of the fluid in saidbulb portion for producing the operational shift of the operating means.

2. The device of claim 1, as a pilot burner safety device: there being apilot burner adjacent the bulb portion, means holding the burner of thebulb portion in position to cause the flame from the pilot burner toimpinge upon the bulb portion; the bulb portion and the connecting tubebeing relatively disposed so as to result in the expulsion of all of theliquid from said bulb portion and to maintain the same out of said bulbportion when the flame is impinging thereon.

3. The device of claim 1, wherein the tube connecting the expansionchamber of the bulb portion connects into the latter at the lowest pointto which liquid within the zone of heating by the burner will gravitate,to provide for a smooth expulsion of liquid from the bulb portion and toprevent the gravitating of liquid baci: into the heated zone.

4. The combination of claim 1, wherein a heater is supported adjacentthe bulb portion, the heater having the capacity to supply sufficientheat thereto to vaporize the liquid in the bulb portion and causeexpulsion of all liquid from the bulb to effect expansion of theexpansion chamber, the heater having a limited area of heating upon thebulb portion so that, after vaporization and expulsion of liquidtherefrom, heat will be applied substantially only to the vapor phase inthe bulb portion, resulting in only relatively small volumetric changesin the system.

5. The combination of claim l, wherein the closed system is entirelyfilled with mercury when the expansion chamber is in a contractedposition.

6. A burner safety device adapted to respond to the existence or absenceof flame under conditions of high ambient temperature: comprising anexpansion chamber, a bulb portion spaced from said expansion chamber, acapillary-type tube connecting the bulb and expansion chamber to form aclosed system, the system being filled with liquid mercury when theexpansion chamber is in a contracted position, a pilot burner connectedto the bulb portion of the device for projecting a flame onto thelatter, and said expansion chamber being sufficiently expansible fromits contracted position to receive the liquid expelled from the bulbportion upon complete vaporiaation therein, whereby a large rapidexpansion or contraction of the expansion chamber occurs as the bulbtemperature varies slightly above or below the boiling point, saidcapillary tube connecting into the bulb substantially at the bottomthereof, and said bulb being positioned relative to said burner so thatthe llame projecting therefrom heats the entire bulb portionsufficiently to cause the liquid-vapor intersurface to be maintainedwithin the capillary tube immediately adjacent the outlet of said bulbportion, and operating means having first and second operatingpositions, and being connected to said expansion chamber to be moved byexpension and contraction thereof, the said operating positions beingseparated sufiiciently to require the large volumetric change resultingfrom a change of state within the bulb portion for producing theoperational shift of the operating means.

CLIFTON A. COBB.

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